Filling method

ABSTRACT

A method for filling vias in an electronic substrate which includes providing a source of fill material; providing a pressure head coupled to the source of fill material via a fill material inlet, the pressure head further comprising an elongated fill material outlet which is substantially larger than the fill material inlet; placing the pressure head in contact with the electronic substrate; and pressurizing the fill material to inject fill material into the vias of the electronic substrate.

This application claims the benefit of U.S. provisional applicationnumber 60/208,454 filed May 31, 2000 and U.S. provisional applicationnumber 60/208,456, filed May 31, 2000 each of which is incorporatedherein by reference in its entirety.

This application is a continuation of allowed application Ser. No.09752,503, filed Dec. 28, 2000, now U.S. Pat. No. 6,506,332.

FIELD OF THE INVENTION

The present invention relates to the field of placing fill materialsinto the vias of an electronic substrate such as by placing electricallyconductive, thermally conductive or nonconductive pastes into and ontoelectronic circuit boards, ceramic substrates and laminate packages.More particularly, this invention deals with placing electricallyconductive, thermally conductive or nonconductive pastes into electronicsubstrate vias that have a very high aspect ratio and small diameters.For future reference we will use the term “substrate” for devices thatcontain vias/cavities to be filled.

BACKGROUND OF THE INVENTION

A common structure in various electronics packages, such as laminatepackages, wired circuit boards, ceramic substrates, and hybrid circuits,is a via. A via is a vertical opening which can be filled withconducting material used to connect circuits on various layers of asubstrate or electronics packages to one another. Vias in certaindevices may connect to a semiconducting substrate. A via generallystarts as an empty cylindrical opening in an electronics package whichis formed by drilling. The via is then plated with an electricalconductor such as copper or tin. Plating may be done over the entirepanel or device, or may be done with a pattern, dot, or button feature.The plating process results in a via that is an opening with a plated,electrically conductive layer on the inner surface of the opening.Plating may also result in plating all or part of the surface of thedevice. Plating of the via provides the primary electrical contact atthe various layers within the device. The following step is to fill thevia with an electrically conductive, thermally conductive ornonconductive paste. The reasons for filling the via after platinginclude providing a secondary or fail safe electrical connection, or toprovide structure integrity, to prevent chemical process entrapment fromdown-line operations, or to provide thermal conductivity to remove heatfrom the inner circuit layers of the resulting device. Another reason isthat filling the via also controls the breaking of electricalconnections formed when the plate or finished electrical devicethermally cycles between operating temperatures and non-operatingtemperatures.

Via filling can occur in the preliminary steps of laminate manufacture,in interim micro-vias, buried vias, blind vias, as well as for pre-goldplate near the end of the end of package/board.

Sequential Build-Up begins with the construction of the “Core Material”,meaning a single or multi-layer copper/resin construction having copperfoil on the top and bottom surface. The foil can be of varied thicknessnoted in terms of ounce weight, ½ oz., ⅜ oz. and the like. The core isnormally mechanically drilled to meet design specifications, de-burred,then cleaned and plated with copper. These plated vias require fillingwith material which will then be covered “capped” with a platedconductive material such as copper.

There are some basic approaches to plating the core panels, such aspanel plate (non-featured surface), button plate, pattern plate and fullbuild; the first three usually distinguished by electrolytic processesand the last an electroless process. We will briefly expand upon thefirst three approaches as examples of how the plating features relate tothe via fill process. Panel plate affords the easiest method ofprocessing of via fills. The entire surface of the panel is plated,including the drilled vias. Because there is no patterned topography,the via fill material can be directly applied to the surface by squeegeecontact or other means without a patterned stencil or screen.

This eliminates the need for extremely accurate registration of astencil to the patterned vias. For both button plate, and pattern plate,a resist image is applied, plated, stripped, then via fill is applied byregistered stencil, sometimes aided by a resist. The reason for theresist: patterned vias have a raised land (annular ring) that can varyfrom 52+ microns wide (typically), and have a thickness of 16 to 52microns. This creates a gasket problem for the stencil, especially whenone has to register to x, y, theta across an 18″×24″ panel. There arepositive and negative aspects for each of these methods. We'll look atthe two most basic ones. Panel plating offers ease of via fillapplication and leveling by means of planarization, but is limiting inits ability to produce the finer features sought for higher circuitdensity. Pattern plate offers the better line-space definition, butcreates intense registration issues with the stenciled via fill process,and exacerbates any overfilling, or resin bleed-out onto surfaces thatmust remain pristine. In Japan, the tendency is to panel plate, and alsoto ease registration issues by reducing panel size. This reducespopulation and profitability per panel as well. Here in the UnitedStates, for the most part manufacturers try all three plate-upprocesses.

The intent is to uniformly plate the drilled via walls at a satisfactoryratio to the core panel's surface. Quite often plating thicknessuniformity can be off, causing varied plated wall thickness, “knee”(excessive plate-up at the top and bottom of the plated via walls).There can also be nodules formed by the plating solution within thevias. These issues can also cause problems with via fill uniformity,especially with the squeegee print filling processes, as material flowis non-uniformly restricted in random vias. The size and depth of thedrilled/plated vias will depend on the number of layers within the corepanel itself. The thicker the panel, and smaller the via diameter, themore difficult the subsequent plating and via filling operation. Thereare planarization steps that can be used to help gain surfaceuniformity, but generally it is best to avoid this step by betterplating bath control.

In terms of via fill processing, currently used application methods maylead to potential defects that might be caused by preparation of thematerials, or the application method itself. The application method andpotential defects will now be discussed.

Squeegee blade application consists of using a metal, polymer, orcomposite blade to force via fill material through the via holes, usinga roll-effect pumping action caused by the squeegee being moved forwardat a given angle to that of the substrate under process. This rolleffect provides a source for air entrapment within the material, whichthen forces the air into the via. For aspect ratios greater than 4:1, itis often necessary to perform multiple passes. This process providesadditional air pockets in the material that are transferred into the viaas voids. Using the squeegee process over bare substrate requires strictcontrol of material volume in front of the squeegee, leaving the processsubject to excess variability in material transfer into the vias, andvarying air bubble entrapment. In addition, large area exposure of thevia fill material may introduce contaminants to the paste. This processnormally exhibits excessive material waste, the need to add more pasteto replenish volume in front of the squeegee, (additional airentrapment), and can lead to divot or material drag-out caused by thetrailing edge of the squeegee, leading to poor leveling. Leveling (bysanding) becomes non-uniform.

Squeegee over imaged resist results in slightly reduced waste, sincethere is less material to planarize. However, this process has the sameproblems as above, with slightly less divot potential. Furthermore,there is a possibility of co-cure of resist, which can lead to stripproblems.

Squeegee over stencil provides slightly improved control over materialwaste and allows two-way printing, but also requires accurateoptics/registration to meet typical theta specification(s) for HDI. Astencil increases the potential for air entrapment. Gasketing over viaannular rings becomes an issue since loss of fluid pressure over a viamay lead to incomplete filling. A single pass fill is required, or anair pocket equal to the stencil aperture volume is forced into the via.

Squeegee over emulsed/imaged screen improves gasketing, but introducespattern stretch. The screen mesh used greatly increases air entrapment.The screen emulsion compatibility with fill material may also be anissue. Registration repeatability becomes more difficult and a singlepass is required to avoid additional air pockets.

As discussed above, the current manufacturing processes associated withfilling vias with paste has several problems. In the past it has beendifficult to reliably place paste in a via without forming an air pocketor void. The via must be completely filled with paste so that there areno air pockets. If there are voids or air pockets in the paste, theseair pockets generally remain in the completed product. A via with a voidhas several adverse effects. If the paste is placed to provide thermalconductivity, the air of the void is an insulator. If the paste isplaced to provide electrical conductivity, if an open should occur atthe void there will be no secondary or fail safe electrical connectionthat can be formed. Furthermore, if the via is filled to providestructural integrity, a void in the via provides for less structuralintegrity.

Among the effects are that air acts as an insulator, not being asconductive as the paste or plating material. As a result, a via with avoid is not as electrically conductive as a via completely filled withconductive materials. The void could also result in an open contact. Inaddition, the void is within the via and cannot be seen, may produce amicro pin-hole which can hold process fluid contaminants. In addition,air acts as an insulator with thermally conductive fill materials, andthe void reduces the thermal conductivity of the filled via. In someinstances, a via that contains an air pocket or void may result in theelectronics package failing to meet manufacturing specifications. Theelectronics package may be rejected. Rework may be possible, but wouldbe time consuming. In other instances, the electronics package may haveto be scrapped which would reduce the yield percentage associated withthe manufacturing process.

The problems set forth above are magnified when a smaller diameter,higher aspect ratio via is required. Smaller diameter, higher aspectratio vias are becoming more popular as the miniaturization ofelectronics packages continues to form more densely populated products.Vias to be filled may range from 2-25 thousandth of an inch in diameterand currently have had a depth to diameter ratio from 1:1 to 10:1. Theindustry struggles to fill vias with aspect ratios greater than 6:1.

Thus, there is a drive to establish a method and apparatus to reliablyfill vias since filled vias provide numerous advantages in thedeveloping HDI (High Density Interconnect) and SBU (Sequential Build-Up)technologies.

In addition, the exponential growth of organic laminate package andboard production has pressed manufacturers to ever increasinginterconnect densities, while shrinking size and cost per unit. A goodexample of this would be the sheer volume growth of throwaway cellphones. Smaller size, lower cost, and performance are critical forcompetitive marketing on a global scale. At the same time, the demandfor filling of via holes has been rising ever since surface mounttechnology (SMT) became a PCB industry standard. Inner layers are oftenfilled by resin flow during lamination, and as with Plastic Land GridArrays (PLGA's), re-flowed solder materials had been used as astructural reinforcement for plated thru-holes, with the added propertyof high conductivity for potentially bridging any opens caused by wallcracking or other defects.

The designers of High Density Interconnect (HDI) boards and HDI or,Sequential Build Up (SBU) packages are now relying on the ability toutilize various via fill materials to enhance reliability andperformance of their designs. The demand, for the most part, had beenfor non-conductive via fill materials. The via fill applications werebasically intended to have two functions; to prevent carry-overcontamination from post-fill processing, and to provide some structuralsupport. Although not a standard industry practice, this applicationdemonstrates an area in which improvements of a via fill material,specifically it's conductivity, will greatly simplify package and boardprocessing. Thus, there is great interest in advantages of thermal andelectrically conductive material use for improved reliability. Combinedwith feature size reduction, the filling of features such asthrough-holes, blind vias, and via in pad with conductive/non-conductivematerials plays an enabling role towards this growth.

In conclusion, there is a need for a method and apparatus for placingpaste into via openings in electronic packages so that there are no airpockets formed in the paste. There is also a need for a process andapparatus which can be used to form a plugged via which has a reliableelectrical contact and which has favorable thermal characteristics.There is also a need for a process which can improve yield for formingplugged vias in electronic packages. There is still a further need for amanufacturing process which is controllable and which has a higherthroughput during manufacturing, such as in a relatively high speed,single pass operation. There is also a need for a process that can beadapted for use with stencil printing machines currently used in themanufacturing process. There is also a need for a device which willlessen the possibility that contaminates will be introduced into the viafill paste. Furthermore, there is a need for a device that can be usedto place paste in vias having high aspect ratios and small diameters.There is further need for an apparatus which has added control forfilling the vias.

SUMMARY OF THE INVENTION

Devices and methods are disclosed for delivering a fill material, suchas electrically and/or thermally conductive paste, and/orelectrically/thermally insulating paste, and/or solder paste to anelectronics package or other planar surface where the delivery systemincludes a pressurized supply of fill material and a pressure headattached to the pressurized supply of fill material. The pressure headincludes a main body and a wear portion. Attached to the wear portion isa gasket positioned along one surface of the pressure head. The pressurehead also includes a flow dispersion regulator which includes apunctured feed tube positioned within the main body, the punctured feedtube has a plurality of flow regulating openings. The flow regulatingopenings in the punctured feed tube are sized to maintain asubstantially constant pressure at each of the flow regulating openings.Positioned between the main body and the wear portion is a flowequalization grid. The flow equalization grid includes a multiplicity ofopenings. Attached to the wear element is a gasket. The pressure sourcemay include one or more hydraulic, pneumatic or mechanically drivenpressurizing cylinders, and may include a ram press for back-fillingpaste vessels. Back-filling is desirable to prevent air entrapmentduring the paste loading process. The paste flow is also controlled witha vacuum pressure release valve. In some embodiments, a controlledoutput ultrasonic driver is attached to the pressure head. An outputcontrol mechanism is used with the ultrasonic driver.

Advantageously, the paste delivery system is an apparatus which employsa method for placing via fill paste into via openings in electronicpackages so that there are reduced numbers of air pockets formed in thevia fill paste while decreasing the amount of processing time requiredper board, providing for the use of a wider variety of fill materials,and minimizing wastage and contamination of fill material. In addition,if air pockets are formed, the air pockets would advantageously haveless volume than the air pockets or voids formed using other methods.The apparatus and related processes preferably result in plugged viaswhich are reliable electrical contacts and have favorable thermalcharacteristics. The process preferably has improved yields forelectronic packages or PCB boards, which use plugged vias. Themanufacturing process preferably is controllable and has a higherthroughput during manufacturing, as is obtained by decreasing the amountof process time required per board. Such decreases in many instances canresult in a process time of less than 30 seconds per board. The processpreferably can be adapted for use with stencil printing machines, and/orscreen printing machines currently used in the manufacturing process.The device preferably utilizes fluid pressure necessary to overcomevaried flow resistance in vias. Furthermore the device preferably usescontact pressure to allow sufficient gasketing on the device underprocess to maintain internal fluid pressure. Furthermore, the devicepreferably provides a combination of gasket and internal fluid pressureto restrict surface air entrapment in the paste. Furthermore, the devicepreferably lessens the chances that contaminates will be introduced intothe via fill paste. Furthermore, the device and process preferably canalso be used to place via fill paste in vias having high aspect ratiosand small diameter with added control for filling the vias. Furthermore,the device preferably can be used for screen-printing resist materialsand/or other conductive/non-conductive materials. Furthermore, it ispreferred that a relatively low fill material pressure is achievable. Itis contemplated that such successful use of lower pressure may resultfrom the use of a flow grid, a dispersion regulator, and the use ofmultiple sequential pressure chambers within the fill head.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a first embodiment of a pastedelivery system for delivering pastes to electronics packages.

FIG. 2 is a side view of the paste delivery system of FIG. 1.

FIG. 2A is a side view of the paste delivery system of FIG. 1 showing apressure head being moved into contact with and along a substrate awayfrom a parking zone.

FIG. 2B is a side view of the paste delivery system of FIG. 1 showing apressure head in contact with a substrate and being moved along thesubstrate and into a parking zone.

FIG. 2C is a side view of the paste delivery system of FIG. 1 showing apressure head being moved within a parking zone and being raised awayfrom a substrate.

FIG. 2D is a schematic side detail view of the pressure head adjustingmechanisms of FIG. 1.

FIG. 2E is a back detail view of the pressure head mounting mechanismsof FIG. 1.

FIG. 2F is a side detail view of the pressure head mounting mechanismsof FIG. 1.

FIG. 3 is a front view of an assembled pressure head of the pastedelivery system of FIG. 1.

FIG. 3A is a front view of an alternative assembled pressure head of thepaste delivery system of FIG. 1.

FIG. 4 is a front exploded front view of the pressure head of FIG. 3.

FIG. 4A is a front exploded front view of the pressure head of FIG. 3A.

FIG. 5 is a side exploded cutaway view of the pressure head of FIG. 3.

FIG. 5A is a side exploded cutaway view of the pressure head of FIG. 3A.

FIG. 6 is a bottom view of a wear element of the pressure head.

FIG. 7 is a bottom view of an alternative wear element of a pressurehead.

FIG. 8 is a top view of a pressure equalizing element of a pressurehead.

FIG. 9 is a side view of a flow dispersion regulator.

FIG. 10A is a view of one of the pressure chambers of a paste deliverysystem for delivering pastes of FIG. 1.

FIG. 10B is a view of a first alternative embodiment of one of thepressure chambers of a paste delivery system for delivering pastes ofFIG. 1.

FIG. 10C is a view of a second alternative embodiment of one of thepressure chambers of a paste delivery system for delivering pastes ofFIG. 1.

FIG. 11 is a showing a pressure head having a controlled outputultrasonic driver.

FIG. 12A is a front view of a second embodiment of a paste deliverysystem.

FIG. 12B is a side view of the of the paste delivery system of FIG. 12A.

FIG. 12C is a top view of the paste delivery system of FIG. 12A.

FIG. 13 shows a paste delivery system incorporating a rolling substratesupport mechanism.

FIG. 14 shows the use of the paste delivery system with a stencil nestedplate for patterned panels.

FIG. 15 shows a third embodiment of a paste dispensing system.

DETAILED DESCRIPTION

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which are shown by way of illustration specific embodiments inwhich the invention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

Overview

FIG. 1 is a schematic perspective view of a first embodiment of a pastedelivery system 100 for delivering paste to a substrate 130 thatincludes at least one via 132. The paste delivery system 100 of thefirst embodiment includes a pressure head 200 attached to a mechanism150 for moving the pressure head 200. The system also comprises a headparking mechanism 190, and a substrate support structure 180.

The pressure head 200 is placed in contact with and moved acrosssubstrate 130 by movement mechanism 150 while fill material is forcedthrough pressure head 200 and into the vias contained in substrate 130.Substrate support structure 180 supports substrate 130 during the fillstation, and head parking mechanism 190 helps prevent loss of fillmaterial between passes of pressure head 200 across substrate 130. Thefill material is forced through as a result of the pressure head 200being coupled via feed tubes 120 and 120′ to a source of pressurizedfill material comprising pressure chambers 141 and 142. Pressure atwhich the source provides fill material may be referred to hereinafterthe fill material pressure.

Pressure Head

FIG. 3 is a front view of an assembled pressure head of the pastedelivery system 100 of FIG. 1. The pressure head 200 includes a mainbody portion 210 and a wear element holding portion 220. Attached to thewear element holding portion 220 is a wear element 230. A flow grid 500is captured (see FIG. 4) between the main body 210 and the wear elementholder 220, and a flow dispersion regulator 132 passes through main body210. The main body 210, wear element holder 220, and possibly wearelement 230 form an elongated narrow pressure chamber 300. FIGS. 4 and 5provide exploded front and cutaway views of the pressure head of FIG. 3,and FIGS. 3A, 4A, and 5A provide similar views of an alternativeembodiment pressure head 200.

The main body 210 and the wear element holding portion 220 may be madefrom any suitable materials, but are preferably made from materials thatwill remain inert with respect to the fill material/via fill paste thatwill pass through the pressure head 200. Examples of such materialsinclude but are not necessarily limited to machine-anodized aluminum,stainless steel, solvent-resistant polymer, and Teflon-impregnatedDelrin. In less preferred embodiments, main body 210 and/or wear elementholding portion may comprise a composite of materials and/or pieces.

Pressure Head—Main Body

In FIG. 4 and FIG. 5, the main body 210 includes a flow dispersionregulator 310 (shown separately in FIG. 9) which passes through and isin fluid communication with a pressure chamber 300. The flow dispersionregulator 310 comprises a punctured feed tube which is preferably alength of stainless steel tubing having a length longer than thepressure chamber 300, and having openings/orifices 311 along its length.

The stainless steel tubing has a first threaded end 312 and a secondthreaded end 314 which extend beyond the main body 210 of the pressurehead. Near end 312 is O-ring 313 which is used to seal end 312 withrespect to the pressure chamber 300. A similar O-ring or seal 315 sealsend 314. Nuts 316 and 317 are attached to the threaded end of the flowdispersion regulator 310. Tightening the nuts 316, 317 seals thepressure chamber 300 and fixes the position of the flow dispersionregulator 310. The threads of ends 312, 314 provide a mechanism forattaching supply lines 120, 120′ to the ends of the dispersionregulator. Fill material from a pressurized source pass through supplylines 120, 120′, through ends 312, 314 into dispersion regulator 310,and out orifices 311 into chamber 300.

It is preferable that the flow path within the dispersion regulatorand/or orifices 311 have varying dimensions so as to equalize thepressure at the various openings while via fill paste passes into thepressure chamber 300. In a preferred embodiment, orifices 311 near theends 312 and 314 are larger than orifices near the center of the mainbody. In essence, the orifices are made smaller, the nearer they are tothe center of the punctured feed tube within the pressure chamber 300since it is recognized that as the paste flows through the flowdispersion regulator 310, a certain amount of pressure headway is lost.To maintain an equal pressure, the orifice size is decreased near thecenter of the flow dispersion regulator 310, so that the force per unitarea or pressure near the center of the flow dispersion regulator 310 issubstantially equal to the pressure found at smaller openings in theflow dispersion regulator near one of the ends 312, 314. The orificescan be placed anywhere along the length of, and can also be placedcompletely around the circumference of the flow dispersion regulator310. In addition, the orifices in the flow dispersion regulator 310 canbe reoriented by loosening the nuts 316, 317 and rotating the flowdispersion regulator 310. Although the, orifices 311 can be facing thewear element portion 220 of the pressure head 200, it is preferred thatthey face away from wear element portion 220 and towards a wall ofchamber 300.

The main body 210 also includes a shoulder 320 which forms a necked-downportion 322. The necked-down portion 322 fits within a similarly sizedand dimensioned opening in the wear element holding portion 220 of thepressure head which includes a land 323. A gasket 324 seals theconnection between the main body 210-and the wear element holdingportion 220. As will be discussed in regard to wear element holder 220,unthreaded opening 352 play a part in coupling wear element holder 220to the main body 210. In the alternative embodiment of FIGS. 4A and 5A,the wear element holder 220 is inserted within main body 200. Yetanother alternative embodiment may utilize a wear element holder 220having a necked down portion similar to that of the main body of FIG.210, the necked down portion fitting within a similarly sized anddimensioned opening in the main body 210 of FIG. 5A.

Looking again at FIG. 4, the openings 212 in main body 210 are formounting the pressure head 200 to guided head support 152 of movementmechanism 150. If the main body 210 is made from a relatively softmaterial such as aluminum, the openings 210 may be provided withhelicoils which are used to provide a threaded opening within a softmaterial and to prevent stripping of the aluminum by a fastener.

Pressure Head—Wear Element Assembly

Wear element 230 is preferably a gasket or O-ring which is attached toan open end of the wear element holder 220. The open end is generallyreferred to by reference numeral 340 as shown in FIG. 6 and FIG. 7.Referring to FIG. 5, the wear element 230 preferably includes a roundedtip 232 which contacts a surface of an electronics package 130, as wellas an end 234 which is captured within a groove 330 within the wearelement holding portion 230. The wear element 230 forms an elongated oroblong opening which can be pressed down to create a suitable seal tothe surface of the electronics package 130, that allows for containedpaste pressure for proper deposition of fill material.

FIG. 6 is a bottom view of the wear element holding portion 230 of thepressure head 200. FIG. 7 shows an alternative embodiments of the wearelement holding portion 230. As can be seen in FIG. 6 and FIG. 7, thewear member 230 comprises one or more elongated and narrow openings 340through which via fill paste or a similar material will pass whenexiting the pressure head 200. It should be noted that the size of theopening(s) 340 can be changed in order to accommodate different patternsof vias on various electronic packages or panels. It is contemplatedthat different wear element holders 220 and/or wear elements 230 havingdifferent sized paste dispensing openings 340 can be attached to asingle main body 210. Thus the wear element holding portion can bechanged to retool a paste dispensing system 100 for different plates orelectronics devices. The size and shape of wear element 230 and wearelement holder 220 should such as to help prevent edge distortion of thesubstrate 130 during application cycles

It is contemplated that the wear element 230 should be made of amaterial that has suitable wear characteristics, yet will seal when afairly low force is applied by the pressure head to the surface of theelectronics package. The wear element is preferably machined from Teflonor cast in a mold with 40 to 120+ durometer hardness polymer, or siliconrubber. The wear member 230 can be resurfaced and configured in variouslengths and shapes to accommodate different sized print areas forinjecting via fill paste to various configurations of vias in electronicpackages or panels 130.

In a preferred embodiment, the wear element holding portion includes athreaded opening 350 which corresponds to an unthreaded opening 352 inthe main body 210 of the pressure head. Fasteners (not shown) passthrough the bore of the unthreaded opening 352 and into the threadedopening 352 to attach the wear element holding portion 230 to the mainbody 210. It should be noted that there are several similar openings 350in the wear element holding portion 230 and several similar unthreadedopenings 352 within the main body 210, each of which receives a fastenerto assemble the pressure head 200. The threaded opening 350 terminatesabove the groove for holding the wear element 230. Several of theopenings 350 in the wear element holder have small extended drill holesthrough to the groove for holding the wear element or O-ring, to allowplacing vacuum into the groove for the purpose of seating the wear part230. The O-ring 230 can be mounted by placing a vacuum on the unthreadedopenings 352 of the main body 210. This produces a vacuum within thegroove 330 into which one end of the wear element 230 fits which aids inthe mounting of the wear element.

Pressure Head—Flow Grid

FIG. 8 is a top view of the pressure-equalizing element or flow grid500. The flow grid 500 is located between the main body 210 and the wearelement holding portion 230 and helps distribute the fluid flow of thevia fill paste or similar material. The flow plate 500 includes amultiplicity of openings 510. As shown in this embodiment, the flowopenings 510 are equally spaced and of approximately the same diameter.It should be understood that the flow plate 500 can have openings 510which are larger or smaller in diameter, and which are in differentpatterns in order to accommodate varied paste rheologies. The flow gridis interchangeable with alternative flow grids so that differentviscosities of via fill paste may be accommodated by use of anappropriate grid.

Flow grid 500 is preferably made of stainless steel and fitted betweenthe main body 210 and the wear element holder 220 of the pressure head200. More specifically, the necked-down portion 322 of the main body 210preferably captures the edge of the flow grid 500 between the main body210 and the wear element 220.

Source of Pressurized Fill Material

Referring to FIG. 1, the source of pressurized fill material ispreferred to comprise a plurality of pressure chambers such as pressurechambers 141 and 142 shown attached to the transverse support member 158in FIG. 1. FIGS. 10A-10C show alternative pressure chamber designscontemplated for use as chambers 141 and 142.

Referring to FIG. 10A, the pressure chamber 141 or 142 of the pastedelivery system 100 includes a backplated ram press chamber whichcomprises a canister 400 having a piston 410, an ‘O’ ring seal 411, anda paste feed out tube 412, and air bleed valve 413. Fill material 100 isplaced into the canister 400, and capped with the piston 410. Pressureis placed on the piston 410, and the paste is forced out of the feed-outtube 412, with the bleed valve 413 temporarily open to evacuate anytrapped air. Once air is removed, the bleed valve 413 is closed,allowing paste flow to the pressure head 200.

Referring to FIG. 10B, an alternative embodiment of the pressure chamber141 or 142 of the paste delivery system 100 includes an air pressurizedcalking gun cylinder chamber having vacuum release capability. Thepressure chamber 141 includes an outer casing 180 and an inner chamber181. The pressure chamber 141 includes an outlet end 183 which isattached to feed tube 120. The pressure chamber 141 is capped with adome-shaped cap 182 which is screwed onto the end of the pressurechamber. The dome-shaped cap includes an air fitting 184. Within theinner chamber 181 is a plunger 186. The plunger is sealed within theinner chamber 181. Paste is positioned between the plunger 186 and theoutlet end 183. The plunger 186 caps contains the paste within the innerchamber of the pressure chamber 141.

The control for pressure is actually two way. During a print stroke orwhen paste is provided to the print head or pressure head 200, pressureis applied to the plunger 186. When a print stroke or pressure iscomplete, and the print head 200, is moved to a staging or parked area192 (see FIGS. 2A-2C), and the flow of pressurized fill material 110 isreversed by placing a slight vacuum on the plunger 186 so that thematerial within the inner casing as well as the paste within the feedline 120 as well as the pressure head 200 retracts slightly. Thisprevents waste of paste.

Referring to FIG. 10C elements of the embodiments of FIG. 10A and FIG.10B may be combined in an embodiment which utilize a stepping motor 420to move a piston 410 having O-ring seal 411 and bleed valve 421. As canbe seen, feed tube 120 is coupled to the “bottom” of the chamber 400.The stepping motor 410 moves piston 410 to force fill material 110 outof chamber 400 and through feed tube 120.

Although fill material 110 may comprise any material which can be usedto pressure fill the vias of a substrate, it is contemplated that theuse of electrically conductive or nonconductive and/or thermallyconductive or nonconductive pastes may be particularly advantageous,particularly in instances where the substrate comprises an electronicspackage member.

Movement Mechanism

The mechanism 150 for moving the pressure head 200 includes a transversesupport member 158, a first rail 156 and a second rail 157, couplingmembers 155, guided head support 152, and head support guide mechanisms151 comprising bearing block 151A and rail 151B. The mechanism alsoincludes a first pneumatic mover 153 attached to one side of a guidedhead support 152 and a second pneumatic mover 154 attached to the otherside of the guided head support 152. The pneumatic movers 153, 154 areused to control the movement of the pressure head 200 with respect tothe support member 158, and are also used to control the amount of forceor pressure between the pressure head 200 and the plate 130. Bearingblock 151A and rail 151B guide and provide lateral support to guidedhead support 152. The support member 158 is slidably connected to thefirst rail 156 and the second rail 157 via coupling members 155.

In alternative embodiments the pressure head 200 can be attached to anycommon screen-printing machine via a transverse bar on the printerswhich replaces support member 158.

The head 200 must be mounted to the movement mechanism 150 in such a wayas to provide uniform planarity with the substrate or surface to beprocessed. Bearing block 151A and rail 151B, by providing lateralsupport to guided head support 152 help prevent “wobbling” of guidedhead support 152 as it is moved up and down by movers 153, 154. Theorientation of pressure head 200 relative to guided head support 152 isaccomplished (referring to FIGS. 2C-2E) via studs/fasteners 161 andleveling screws 162. Studs 161 are preferably screwed into or otherwisefixed in pressure head 210 and extend outward from the head throughslots 163 in guided head support 152. Leveling screws 152 are preferablyscrewed into guided head support 152 and abut pressure head 200. The useof such studs and leveling screws allows the head to be positionedvertically by sliding the studs 161 up and down within slots 163, andallows the orientation of pressure head 200 relative to guided headsupport 152 to be adjusted through a combination of ration of theleveling screws 162 and tightening the pressure head 200 against thescrews 162 via studs/fasteners 161.

Head Parking Mechanism and Substrate Support Structure

Head parking mechanism 190 preferably comprises a ledge 192 having abeveled edge 193, and independently sliding ledge support members 192Aand 192B. Ledge 192 may comprise any relatively stiff, flexible materialsuch as a spring steel.

Operation

A substrate 130 is positioned on a support structure 180 (which maycomprise a first member 181 coupled to a second member 182 upon whichthe substrate is positioned), ledge support member 192A is slid upagainst substrate 130 so as to essentially extend the upper surface ofsubstrate 130 and raise ledge 192 to the height of substrate 130, andledge support member 192B is slid towards substrate 130 so as to movethe edge 193 of ledge 192 off of support member 192B and onto substrate130. When thus positioned, ledge 192 protects any tooling holes near theedge of substrate 130 which are not to be filled, and provides amechanism by which the pressure head 200 may be moved onto off ofsubstrate 130 with minimal loss of fill material 110.

Once the substrate is positioned, the pressure head is positioned sothat the wear element 230 is in sealing contact with substrate 130 andsurrounds one or more vias 132. Positioning the wear element in contactwith substrate 130 is accomplished via pneumatic movers 153, 154 whichmaintain a specific force between the wear element 230 and the substrate130, and by movement of support member 158 along rails 156, 157.

Pressure is then applied to the source of fill material so as to causethe fill material to flow through feed tubes 120 and 120′, throughpressure head 200, out opening(s) 340, and into vias 132. Morespecifically, the pressure mechanism 141 produces a pressure within thefeed line 120 which is attached to the pressure head 200. Thepressurized paste flows through the feed lines 120, 120′ into the flowdispersion regulator 310 in the pressurized chamber 300 of the pressurehead 200. The pressure is equalized by the orifices or openings, such as311, within the flow dispersion regulator 310 in the pressurized chamber300. After entering the pressurized chamber 300, the paste then flowsthrough the flow-equalizing grid 500 and into the opening 340 in thewear element holding portion 220. From opening 340 it flows against thesurface of substrate 130 sealed against head 200 and into vias 132.

As the vias 132 are filled, the pressure head is moved to anotherlocation on the electronics package where there are additional vias.Such movement is accomplished as engagement between pressure head 200and panel 130 and flow of pressurized fill material 110 is maintained,and the support member 158 is moved along the rails 156 and 157 to causethe pressure head 200 to move across the panel 130. As the head 200remains in engagement with the substrate 130, a more or less continuousamount of pressurized fill material 110 flows from the pressure sourcethrough the feed lines 120, 120′ and into the pressure head forinjection into the vias 132 within the substrate 130.

Movement of pressure head 200 is towards parking ledge 192 of parkingmechanism 190. The ledge 192 includes a slight beveled edge 193 so thatthe head 200 can be moved across the panel and onto the ledge 192 into apark position with minimal loss of fill material. When the head 200 ispassed to the park position, the flow of pressurized fill material isreversed (i.e. a vacuum release is applied) to retract any paste thatmay flow from the pressure head if/when the head is subsequently raisedoff of the ledge 192.

While the pressure head 200 is positioned on ledge 192, the panel 130that has filled vias is removed from the support structure 180 andanother panel is placed on the support structure 180. The process forfilling the vias then repeats.

The fluid pressure of the fill material 110 and vacuum release can becontrolled either manually or by tying it to a stop-activated switch setto specific substrate print length. In another embodiment (see FIG.12A), a machine vision system can be substituted for the stop-activatedswitches. The machine vision system would produce a signal when theselected via pattern area has been filled.

Use of Pressure Head with an Ultrasonic Driver

FIG. 11 is a schematic showing an embodiment of pressure head 200 havinga controlled output ultrasonic driver system 800. Several ultrasonicdrivers 810, 812, 814, 816 are attached to the main body 210 of thepressure head 200. Communicatively coupled to the ultrasonic driver isan output control system 820. The output control system 820 providessignals to the ultrasonic driver 810 which regulate the frequency andmagnitude of the ultrasonic vibrations provided to the pressure head200. The output control 820 may include a microprocessor and a feedbackloop.

The ultrasonic drivers 810, 812, 814 and 816 are vibrated at a frequencywhich will not cure the via filling paste 110. By applying ultrasonicvibrations to the via filling paste 110, very high aspect ratio vias 132may be filled. For example, even with fill materials that are verydifficult to process vias 132 having an aspect ration of 12:1 can befilled without ultrasonic drivers 810, 812, 814 and 816, and vias 132with aspect ratios up to 17:1+ can be filled using the ultrasonicdrivers. It is contemplated that even higher aspect ratio vias may befilled using a pressure head 200 provided with ultrasonic drivers 810,812, 814 and 816. It is believed that very high aspect ratio via fillingis also dependent on paste rheology, solids loading, and particle sizedistribution within the paste.

Structure and Operation of a Bottom Fill Embodiment

In alternative embodiments, pressure head 200 may be positioned so thatfill material 110 is forced upwards into vias 132 of substrate 130. Onesuch “bottom fill” embodiment (i.e. a process which requires the viafill paste 110 to overcome the forces of gravity) is shown in FIGS. 12A,12B, and 12C. In this particular embodiment, a “stationary” pressurehead 200 is positioned below a split conveyor having two portions 105,105′. The panels or electronics packages 130 are pulled over aninjection head 200 and then exit on the opposing side where the panel orelectronic package is removed and a fresh panel is loaded for viafilling in a continuous fashion. This second embodiment will have a highthroughput since plates or electronics packages 130 can be continuouslyfed and filled using this system. The pressure head 200 does not move asmuch as in the first embodiment. In the second embodiment, the pressurehead 200 moves up and down or into and out of engagement with the panel200. The panels 130 are moved over the pressure head 200 as the vias arefilled.

The pressure head raises by activating a pneumatic, two-sided pressurecylinder 920 having adjustable up-and-down travel of approximately 1 to3 inches to meet the panel surfaces or electronic package 130 surfacesto be filled. The two sided pressure cylinder 920 is attached to aguided head supporting bar 952 as is head 200 A first scavenger blade960 is positioned on one side of the panel and a second scavenger blade1020 is positioned on the other side of the panel 130.

Advantageously, a bottom fill process allows in-process observation offill hole quality and eliminates the need for stop-off sheets, orstand-offs as used for overfill that occurs during top-side filling.Thus, the scavenger blade 960 may not be necessary when using the bottomfill process. The in-process observation of via fill quality can be doneby the naked eye or can be observed using a vision system 950 as shownin FIG. 12A. An additional advantage is that there is less possibilityfor air pockets or voids formed in the vias 132 of the electronicspackages or panels 130.

Scavenger blade 1020 is mounted on the pressure head 200 in order tominimize downstream planarizing processes. Planarizing of the entiresubstrate surface would still normally be required, in order to providea level surface for subsequent plating processes, i.e. copper capping ofthe filled vias. It should be noted that the up-and-down or Z directionmotion (contact force, the filling pressure (internal head fluidpressure), and cycle speed over the substrate are directly related tothe substrate via pattern size, diameter & aspect ratio of the vias tobe filled.

Now turning to FIG. 13, it can be seen that on the side opposite of thepanel, opposite the pressure head 200, a set of rollers or wheels havingrandomly spaced contact wheel array 1000 between the fill patterns areprovided. Wheel arrays 1000 are in immediate proximity to the fill area1010 of the electronic package or panel 130 being filled. The wheelarrays 1000 prevent or lessen warped or distorted panels that mightresult in unsupported filling using the pressure head 200.

Structure and Operation of a Stencil-Nested Plate Embodiment

FIG. 14 is a another embodiment of a paste delivery system 100 showing anested plate 1110 used with a stencil 1100 for patterned substrates 130.Nested plate 1110 mates with a stencil 1100 and has conical tooling pins1111 to allow a panel or electronics package 130 to be registered to thestencil. The substrate is shuttled through or past a fixed injectionhead in a similar manner as described in the embodiment of FIGS. 12A,12B, and 12C. This particular procedure allows for pattern-plated coresand/or finished billed via filling.

Structure and Operation of a Syringe Pressure Source Embodiment

FIG. 15 shows yet another embodiment of a paste-dispensing system 1300.In this particular system, via fill paste or via fill paste is within asyringe-type device 1310. Air pressure is used to move or pressurize thevia fill paste 110. Such a system might be used for small custom jobssuch as building prototype plates. In addition, such a system could beused to provide rework to plates that might contain a slight defect in avia 132 on the plate.

Some Contemplated Advantages

Advantageously, the paste delivery system of the present invention ispreferably an apparatus which employs a method for placing via fillpaste into via openings in electronic packages so that there are reducednumbers of air pockets formed in the via fill paste while decreasing theamount of processing time required per board, providing for the use of awider variety of fill materials, and minimizing wastage andcontamination of fill material. In addition, if air pockets are formed,the air pockets have less volume than the air pockets or voids formedusing other methods. As a result, the apparatus and related processresult in plugged vias which are reliable electrical contacts and havefavorable thermal characteristics, and the process has improved yieldsfor electronic packages which use plugged vias.

The manufacturing process is controllable and has a relatively highthroughput during manufacturing. Such high throughput is obtained bydecreasing the amount of process time required per board. Such decreasesin many instances can result in a process time of less than 30 secondsper board.

The device can lessen the chances that contaminates will be introducedinto the via fill paste. The reduced chance of introduction ofcontaminates is contemplated as resulting from providing a sealed flowpath for the fill material from the fill material source to the viabeing filled.

Furthermore, the device and process can also be used to place via fillpaste in vias having high aspect ratios and small diameter with addedcontrol for filling the vias. Fillable vias 132 can have diameters inthe range of {fraction (2/1000)}ths of an inch to {fraction (25/100)}thsof an inch in diameter. Preferably the diameters are less than {fraction(12/1000)}ths of an inch. More preferably the diameters are less than{fraction (8/1000)}ths of an inch, and most preferably the diameters areless than {fraction (6/1000)}ths of an inch. In addition, the aspectratio associated with these vias, i.e. the ratio of the via depthdivided by the via diameter, that can be filled are from 1:1 to 17:1+,depending on material rheology, paste solids loading, and particle sizedistribution within the paste used. Preferably the aspect ration isgreater than 5:1. More preferably the aspect ratio is greater than 10:1,and most preferably the aspect ration is greater than 12:1.

Advantageously, the fill system utilizes a lower fill material pressureto fill vias. It is contemplated that such successful use of lowerpressure may result from the use of a flow grid, a dispersion regulator,and the use of multiple sequential pressure chambers within the fillhead. It is also contemplated that the use of a fill material outlets(such as open end 340) which are substantially larger than fill materialinlets (such as ends 312 and 314 of the flow dispersion regulator 310)may also contribute significantly to lowering the fill material pressurerequired to adequately fill the vias. It is possible that the largeroutlets and multiple changes in fill material flow direction through thehead provided at least in part by the flow grid, dispersion regulator,and multiple sequential pressure chambers coupled with the viscosity ofthe fill material act to deter flow of the material backwards throughthe head and possibly thus contribute to a decreased fill materialpressure.

It should be noted that substrates 130 can be of any type. For example,plates or electronics packages containing vias may be used even if suchplates or packages comprise laminates or ceramics. In addition, vias inwired circuit boards may also be filled using one or more of theembodiments discussed herein.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. A method for filling vias in an electronicsubstrate comprising: providing a source of fill material; providing apressure head coupled to the source of fill material; placing thepressure head in contact with the electronic substrate; and pressurizingthe fill material to inject fill material into the vias of theelectronic substrate; wherein the pressure applied to the fill materialis less than L pounds per square inch where L is
 80. 2. The method ofclaim 1 wherein L is one of 50, 25, 20, 15, and
 10. 3. The method ofclaim 1 wherein the pressure head comprises a pressure chamber andpressurizing the fill material to inject fill material into the vias ofthe electronic substrate results in fill material flowing into thepressure chamber in a direction away from the substrate being filled. 4.The method of claim 3 wherein the pressure chamber is elongated and fillmaterial flows into the pressure chamber from a plurality of inletsspaced along the length of the pressure chamber.
 5. The method of claim4 wherein the fill material is hindered from flowing out the fillmaterial outlet from the fill chamber by a resistance member positionedwithin the pressure chamber between the plurality of inlets and the fillmaterial outlet, the resistance member dividing the pressure chamberinto at least two parts.
 6. The method of claim 5 herein the fillmaterial flows through a plurality of openings in the resistance member,the plurality of openings being regularly spaced in an areasubstantially equal in size to that of the fill material outlet.
 7. Themethod of claim 6 wherein the resistance member is a flow equalizationspaced adjacent to the fill material outlet.
 8. The method of claim 7further comprising the step of sealing the interface between thepressure head and the electronic substrate by pressing a gasket on thepressure head surrounding the fill material outlet against theelectronic substrate.
 9. The method of claim 8 further comprising movingthe pressure head and electronic substrate relative to each other whilemaintaining the pressure seal between the pressure head gasket and theelectronic substrate and maintaining the pressure of the fill materialsuch that fill material continues to flow into the vias of theelectronic substrate.
 10. The method of claim 9 wherein the total timerequired to fill all of the vias of the electronic substrate to befilled is less than T seconds wherein T is one of 20, 30, 40, and 50.11. The method of claim 10 wherein the movement of the pressure head andelectronic substrate relative to each other is a result of holding thepressure head in a fixed position and moving the electronic substrate.12. The method of claim 11 wherein the electronic substrate is anelectronics package and the step of moving the electronic substratefurther comprises the steps of: supporting a first end of theelectronics package; and supporting a second end of the electronicspackage; and wherein the step of placing the pressure head includesplacing the pressure head between the first end and the second end ofthe electronics package and on one side of the electronics package. 13.The method of claim 12 further comprises the step of supporting a sideof the electronics package opposite the electronic substrate to preventdamage to the electronics package by placement of the pressure head. 14.The method of claim 13 wherein the step of placing the pressure headincludes placing the pressure head such that paste entering a via mustovercome gravitational forces.
 15. The method of claim 14 furthercomprising the step of observing the paste with an automated machinevision system as it fills a via from the opposite side where thepressure head is placed.
 16. The method of claim 15 further comprisingultrasonically vibrating the fill material and/or the pressure headwhile injecting fill material into the vias of the electronic substrate.17. The method of claim 1 wherein the pressure head has an elongatedpressure chamber and a fill material outlet; and pressurizing the fillmaterial forces the fill material into the pressure chamber through aplurality of inlets spaced along the length of the pressure chamber, outthe fill material outlet, and into at least one via of the electronicsubstrate.
 18. The method of claim 17 further comprising forcing thefill material in the pressure chamber to flow through a flowequalization grid spaced adjacent to the fill material outlet and thenout of the pressure head through the fill material outlet.
 19. Themethod of claim 1 wherein all the vias of the electronic substrate arefilled in less than T seconds where T is
 50. 20. The method of claim 1wherein all the vias of the electronic substrate are filled in less thanT seconds where T is 20.